The Privy Council and the Queen have sanctioned the use, if necessary, of contingency powers to control the distribution of fuel across the UK.

The moves came as thousands of petrol stations across the country ran dry as refineries were hit by blockades.

What powers have been granted?

Under section three of the Energy Act 1976, the government can be granted exceptional powers to control the supply of fuel across the country.

Should ministers choose to use these powers, they can direct oil companies to designate petrol stations to supply emergency and essential services only.

Services deemed "essential" include

schools

public transport

food delivery lorries

Although the act allows for military intervention, the government has ruled out bringing in soldiers to assist the police officers currently marshalling the protests.

When will a decision be taken?

Downing Street has said there will be series of meetings throughout the day on Tuesday, involving Mr Blair and other ministers, to decide whether to invoke the powers granted by the Privy Council.

Have these powers ever been used before?

Not according to the Department of Trade and Industry.

The act dates from 1976, just a few years after the OPEC oil crisis in which the pumps ran dry. At the same time, the powerful miners' union refused to do overtime in a dispute over pay. The strike led to the downfall of the Heath administration.

No, says the Association of Chief Police Officers. The protests have been peaceful and the demonstrators are deliberately not blocking the roads.

Sir John Evans, the association's president, has said that should the protesters turn violent, or use intimidatory tactics to block access to and from the refineries, the police will intervene.

What is preventing the petrol stations from replenishing their stocks is the tanker drivers' reluctance to cross the picket lines, and the oil companies are unwilling to force them to fill up.

Peter Norbury, an employment lawyer with the firm Eversheds, says that should the oil companies decide to change their position, tanker drivers could not legally refuse to cross the line.

"The people outside the refineries have no official position at all - it is not a trade union-organised protest.

"Therefore the drivers would be putting themselves at risk of disciplinary action."

What is the Privy Council?

A panel of senior politicians, including all the party leaders, who along with judges and church dignitaries advises the Queen.

It is the oldest form of legislative assembly still functioning, with its origins dating from the Norman kings' court.

Today, the council provides formal advice to the monarch on granting orders in council, such as that used to invoke the emergency powers, and proclamations, which cover coinage, the dates of certain bank holidays, and the dissolution of parliament.